JOINs are left-associative

Change-Id: I24fdd2ce9bb87cc52a7c84ec8cd300bc13b11461
Reviewed-on: https://gerrit.libreoffice.org/10057
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>